Quantitation of normal development of the autonomic nervous system will proceed in parallel with study of neuronal and axonal changes in the sudden infant death syndrome (SIDS) and familial dysautonomia (FD). (FD is a disease in which sudden respiratory arrest is a frequent mode of death and in which we have found neuronal and axonal depletions in sensory and autonomic motor systems.) Specific structures to be studied include autonomic sympathetic and parasympathetic ganglia, sensory ganglia of spinal roots, sensory ganglia of the vagus and glossopharyngeal nerves and the intermediolateral gray columns of spinal cord. Nerves studied will be the vagus and phrenic. Central neuronal groups will be identified immunohistochemically using the peroxidase-anti-peroxidase technique which we are now using to detect neurotransmitter synthetic enzymes. Qualitative and quantitative changes will be sought in these structures. Diaphragmatic and other skeletal muscle will be examined histochemically for evidence of denervation. Morphological changes during normal development will be compared with progression of function. Data from FD and SIDS patients will be analyzed for variations from normal. The relationship of any such variations to clinical syndromes and pathologic etiology will be examined.